1. Field of the Invention
This invention relates to synthetic polyphenol monomers and oligomers, derivatives thereof, and methods for making and using the same.
2. Related Background Art
Polyphenols are a highly diverse group of compounds (Ferreira, D., Steynberg, J. P., Roux, D. G. and Brandt, E. V., Tetrahedron, 48, (10), 1743-1803 (1992)) which widely occur in a variety of plants, some of which enter into the food chain. In many cases, they represent an important class of compounds present in the human diet. Although some of the polyphenols are considered to be non-nutritive, interest in these compounds has arisen because of their possible beneficial effects on health.
For instance, quercetin (a flavonoid) has been shown to possess anticarcinogenic activity in experimental animal studies (Deschner, E. E., Ruperto, J., Wong, G. and Newmark, H. L., Carcinogenesis, 7, 1193-1196 (1991) and Kato, R., Nakadate, T., Yamamoto, S. and Sugimura, T., Carcinogenesis, 4, 1301-1305 (1983)). (+)-Catechin and (−)-epicatechin (flavan-3-ols) have been shown to inhibit Leukemia virus reverse transcriptase activity (Chu S.-C., Hsieh, Y.-S. and Lim, J.-Y., J. of Natural Products, 55, (2), 179-183 (1992)). Nobotanin (an oligomeric hydrolyzable tannin) has also been shown to possess anti-tumor activity (Okuda T., Yoshida, T., and Hatano, T., Molecular Structures and Pharmacological Activities of Polyphenols—Oligomeric Hydrolyzable Tannins and Others—Presented at the XVIth International Conference of the Groupe Polyphenols, Lisbon, Portugal, Jul. 13-16, 1992). Statistical reports have also shown that stomach cancer mortality is significantly lower in the tea producing districts of Japan. Epigallocatechin gallate has been reported to be the pharmacologically active material in green tea that inhibits mouse skin tumors (Okuda et al., ibid.). Ellagic acid has also been shown to possess anticarcinogen activity in various animal tumor models (Boukharta M., Jalbert, G. and Castonguay, A., Efficacy of Ellagitannins and Ellagic Acid as Cancer Chemopreventive Agents—Presented at the XVIth International Conference of the Groupe Polyphenols, Lisbon, Portugal, Jul. 13-16, 1992). Proanthocyanidin oligomers have been disclosed (JP 4-190774) by the Kikkoman Corporation for use as antimutagens. The use of phenolic compounds in foods and their modulation of tumor development in experimental animal models has been recently presented at the 202nd National Meeting of The American Chemical Society (Phenolic Compounds in Foods and Their Effects on Health I, Analysis, Occurrence & Chemistry, Ho, C.-T., Lee, C. Y., and Huang, M.-T editors, ACS Symposium Series 506, American Chemical Society, Washington, D.C. (1992); Phenolic Compounds in Foods and Their Effects on Health II. Antioxidants & Cancer Prevention, Huang, M.-T., Ho, C.-T., and Lee, C. Y. editors, ACS Symposium Series 507, American Chemical Society, Washington, D.C. (1992)).
Procyanidin polyphenols, and particularly higher oligomers thereof, have recently been found to possess a broad spectrum of biological activity Reference is made to U.S. patent application Ser. No. 08/709,406 filed Nov. 6, 1996, now U.S. Pat. No. 6,015,913 issued Jan. 18, 2000 and U.S. application Ser. No. 08/3 17,226 filed Oct. 3, 1994, now U.S. Pat. No. 5,554,645 issued Sep. 10, 1996, each of which is incorporated herein by reference. These patents disclose a variety of health benefits provided by procyanidin polyphenols as well as a means of increasing the concentration of these beneficial polyphenols in extracts, foods, pharmaceutical preparations and chocolate compositions. Reference is also made to parent U.S. application Ser. No. 08/948,226 filed Oct. 9, 1997, now U.S. Pat. No. 6,207,842 issued Mar. 27, 2001, which discloses methods of preparing polyphenol oligomers, and specifically procyanidin polyphenols, the disclosure of which is also incorporated herein by reference.
Isolation, separation, purification, and identification methods have been established for the recovery of a range of procyanidin oligomers for comparative in vitro and in vivo assessment of biological activities. For instance, anti-cancer activity is elicited by pentameric through decameric procyanidins, but not by monomers through tetrameric compounds. Currently, gram quantities of pure (>95%) pentamer are obtained by time-consuming methods which are not satisfactory for obtaining a sufficient quantity of the pentamer for large scale pharmacological and bioavailability studies. Even greater effort is required to obtain gram quantities of higher oligomers, hexamers through dodecamers, for similar studies since they are present in the natural product in much lower concentrations than the pentamer. Additionally, increasing oligomeric size increases structural complexity. Factors such as differences in the chirality of the monomeric units comprising the oligomer, different interflavan bonding sites, differences in the chirality of the interflavan bonding, dynamic rotational isomerization of the interflavan bonds, and the multiple points of bonding at nucleophilic centers pose efficiency constraints on current analytical methods of separation and purification for subsequent identification.
These collective factors point to a need for synthesis methods to permit the unambiguous proof of both structure and absolute configuration of higher oligomers, to provide large quantities of structurally defined oligomers for in vitro and in vivo assessment and to provide novel structural derivatives of the naturally occurring procyanidins to establish the structure-activity relationships of these materials. Accordingly, it would be advantageous to develop a versatile synthetic process capable of providing large quantities of any desired polyphenol oligomer.